1. Field of the Invention
This invention relates to desktop electronic laser printers and more particularly to removable/replaceable toner cartridges for use with such laser printers.
2. Background Information
Laser printers use a focused light beam to expose discrete portions of an image transfer drum so that these portions attract printing toner. Toner is a mixture of pigment (typically carbon black) and plastic. The toner becomes electric statically attracted to exposed portions of the image transferred drum. As a transfer medium such as paper is passed over the rotating image transferred drum, some of the toner is laid onto the medium. Subsequently, the medium passes through a heated fuser so that the plastic is melted into permanent contact with the underlying medium.
The vast majority of desktop laser printers currently available utilize replaceable toner cartridges that incorporate an image transfer drum, a toner tank and a metering system and a drive mechanism for the drum and metering system. Modern toner cartridges often include a variety of sensors that interact with the laser printer in order to indicate the status of the cartridge. Indications relating to toner level, print quality and general cartridge function are often included. A large number of types and sizes of toner cartridges are currently available. Each cartridge is provided with its own set of operating perimeters and toner fill limitations. Certain cartridges, such as the Optra(copyright) S 4019/4039/4049 cartridge, available from Lexmark(copyright) utilize a complex sensing system for cartridge performance. The sensing system includes an encoder wheel interconnected with a rotating agitator blade within a cylindrical toner tank. Movement of the agitator blade feeds toner into the metering system. The encoder wheel reports the movement of the agitator wheel through the toner reservoir. The resulting signal must fall within certain perimeters, or a variety of error conditions are indicated by the printer, and print engine operation may suddenly cease.
The strict limits placed upon this cartridge, and others, can prove difficult to overcome for manufacturers seeking to provide a higher-capacity toner tank for compatible cartridges. This is because, manufactured and remanufactured cartridges must include no more than the original manufacture (OEM) toner level even if a higher level can be provided with appropriate performance. A higher level causes the agitator blade to move differently through the reservoir, thereby sending an erroneous signal to the printer.
Accordingly, it is an object of this invention to provide an extended life toner cartridge that enables a larger-capacity reservoir of toner to be utilized with cartridges having discreet, reduced, capacity limitations based upon internal sensors. This cartridge should enable an enlarged toner tank to be placed in the cartridge thereby extending the capacity of the overall toner reservoir.
This invention overcomes the disadvantages of the prior art by providing an extended life-toner cartridge that provides a set of required agitator paddle movement signals that fall within the expected parameters of the print engine controllerxe2x80x94notwithstanding a higher toner level that would normally alter the paddle movement signals beyond acceptable timing ranges. The cartridge includes a toner tank agitator paddle assembly with a paddle movement reporting mechanism that particularly compensates for the larger volume of toner in the tank. In addition, the toner tank can include an enlarged tank extension for increasing reservoir capacity.
According to a preferred embodiment the agitator paddle assembly includes a timing gear assembly operatively connected to the print engine drive motor. The timing gear assembly includes a stop that enables the agitator paddle to become spring-loaded through a set amount of rotation until it engages a stop that limits further movement of the agitator blade with respect to the timing gear assembly. In a preferred embodiment the movement of the agitator paddle is limited to a greater extent than movement of the OEM agitator paddle. The agitator paddle assembly also includes an encoder wheel, rotationally fixed to the agitator paddle axle that generates a sensor signal equivalent to the encoder wheel of an OEM cartridge in the presence of a larger toner capacity.
According to the preferred embodiment, the encoder wheel includes a series of slots that pass through an optical sensor so as to generate time-variable pulses as the agitator paddle is rotated around the toner tank. The slots include multiple set of closely spaced slots, preceded by an elongated slot that are encountered as the paddle prepares to engage the toner supply. Also provided is a dwell area that is free of slots following the multiple slots. This area is encountered as the timing gear causes the paddle spring to wind until the stop drives the paddle into the toner supply. An additional set of slots then reports movement through the toner supply. The spring causes a snap-back motion of the paddle into the free space as it reaches the top of the toner supply near the cartridge developer section. In the preferred embodiment, the slots are offset and lengthened as appropriate to provide the desired expected timing sequence to the controller in the presence of a higher toner level that causes the paddle to engage the toner, and wind the spring earlier in the rotation cycle.